Identifying public safety answering point (psap) callbacks in internet protocol (ip) multimedia subsystem (ims) emergency services

ABSTRACT

A method and apparatus for identifying public safety answering point (PSAP) callbacks by transmitting, by a wireless transmit/receive unit (WTRU) in a first network, a registration message, to a PSAP in a second network. Upon registration, the WTRU receives a registration response including an information element (IE) and stores the IE. The PSAP, which may be located in either an internet protocol (IP) Network or a public switched telephone network (PSTN), transmits an emergency callback to the WTRU and includes the IE.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/433,053 filed on Jan. 14, 2011, the contents of which are herebyincorporated by reference herein.

BACKGROUND

A public safety answering point (PSAP) may send an callback to a devicethat initiated an emergency call. The callback may occur for a varietyof reasons such as the call being cut short or the PSAP may needadditional information to react to the emergency appropriately. A PSAPcallback is treated as a normal incoming call, which may be subject toservices such as call forwarding that may interfere with the callbackreaching the appropriate device. In addition, determining which deviceplaced the emergency call may be difficult. Accordingly, it would beadvantageous to identify the emergency caller by network and device inorder to ensure the callback reaches its destination.

SUMMARY

A method and apparatus for identifying public safety answering point(PSAP) callbacks by transmitting, by a wireless transmit/receive unit(WTRU) in a first network, a registration message, to a serving callsession control function (S-CSCF) in a second network. Uponregistration, the WTRU receives a registration response including aninformation element (IE) and stores the IE. The received IE is includedin an emergency call transmitted to a PSAP. The PSAP, which may belocated in either an internet protocol (IP) Network or a public switchedtelephone network (PSTN), transmits an emergency callback to the WTRUand includes the IE.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented;

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A;

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A;

FIG. 2 is a block diagram of an emergency services architecture;

FIG. 3 is a call flow diagram of an example of a registration procedureincluding a emergency indicator for callback;

FIG. 4 is a call flow diagram of an example of a usage of theregistration procedure including an emergency indicator for callback;

FIG. 5 is a call flow diagram of an example of call back from a PSAPbased network using an emergency indicator; and

FIG. 6A and FIG. 6B are a flow diagram of callback from a PSTN basednetwork using an emergency indicator.

DETAILED DESCRIPTION

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, 102 d, a radioaccess network (RAN) 104, a core network 106, a public switchedtelephone network (PSTN) 108, the Internet 110, and other networks 112,though it will be appreciated that the disclosed embodiments contemplateany number of WTRUs, base stations, networks, and/or network elements.Each of the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it will be appreciated that the basestations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it will be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 106, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It will be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 106 and/or the removable memory 132.The non-removable memory 106 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It will be appreciated that the WTRU 102 mayacquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 104 and the core network 106according to an embodiment. The RAN 104 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 102 a, 102 b, 102 c over the air interface 116. As will be furtherdiscussed below, the communication links between the differentfunctional entities of the WTRUs 102 a, 102 b, 102 c, the RAN 104, andthe core network 106 may be defined as reference points.

As shown in FIG. 1C, the RAN 104 may include base stations 140 a, 140 b,140 c, and an ASN gateway 142, though it will be appreciated that theRAN 104 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 140 a, 140 b,140 c may each be associated with a particular cell (not shown) in theRAN 104 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 116. In oneembodiment, the base stations 140 a, 140 b, 140 c may implement MIMOtechnology. Thus, the base station 140 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a. The base stations 140 a, 140 b, 140 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 142 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 106, and the like.

The air interface 116 between the WTRUs 102 a, 102 b, 102 c and the RAN104 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, 102 cmay establish a logical interface (not shown) with the core network 106.The logical interface between the WTRUs 102 a, 102 b, 102 c and the corenetwork 106 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 140 a, 140 b,140 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 140 a, 140 b,140 c and the ASN gateway 215 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs102 a, 102 b, 100 c.

As shown in FIG. 1C, the RAN 104 may be connected to the core network106. The communication link between the RAN 104 and the core network 106may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 106 may include a mobile IP home agent(MIP-HA) 144, an authentication, authorization, accounting (AAA) server146, and a gateway 148. While each of the foregoing elements aredepicted as part of the core network 106, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, 102 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 144 may provide the WTRUs 102 a, 102b, 102 c with access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand IP-enabled devices. The AAA server 146 may be responsible for userauthentication and for supporting user services. The gateway 148 mayfacilitate interworking with other networks. For example, the gateway148 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 148 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the networks 112,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 1C, it will be appreciated that the RAN 104may be connected to other ASNs and the core network 106 may be connectedto other core networks. The communication link between the RAN 104 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 102 a, 102 b, 102 cbetween the RAN 104 and the other ASNs. The communication link betweenthe core network 106 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

A public safety answering point (PSAP) may send a callback to a devicethat initiated an emergency call. The callback may occur for a varietyof reasons, such as the call being cut short or the PSAP may needadditional information to react to the emergency appropriately. A PSAPcallback is treated as a normal incoming call, which may be subject toservices, such as call forwarding, that may interfere with the callbackreaching the appropriate device. A need to identify the emergency callerby the network and device in order to ensure the callback reaches itsdestination would be advantageous.

FIG. 2 is a block diagram 200 of an example of emergency servicesarchitecture. Architecture and procedures are required for handlingemergency calls over the IMS. The architecture and procedures ensurethat an emergency call initiated by an IMS WTRU is handled by thevisited network, whether or not the visited network is the WTRU's homenetwork. When a WTRU is roaming, it may be inappropriate for anemergency call to be routed to the WTRU's home network, which may be ina different geographic location than the WTRU.

Referring to FIG. 2, the proxy call session control function (P-CSCF)P-CSCF 210, emergency call session control function (E-CSCF) 215,location retrieval function (LRF) 220 and emergency access transferfunction (EATF) 235 may be located in a visited network. The E-CSCF 215and P-CSCF 210 may act as proxies for the WTRU 205 in order to transmitSIP requests.

The P-CSCF 210 may also be responsible for security between the WTRU 205and itself. The Gm reference point 264 is a SIP-based reference pointbetween the WTRU 205 and the P-CSCF 210. The P-CSCF 210 is the initialSIP signaling contact point for the WTRU 205. The P-CSCF 210 isresponsible for forwarding SIP registration messages from the WTRU 205,to a CSCF (I-CSCF) 275. The I-CSCF 275 may determine a suitable servingCSCF (S-CSCF) 230 for the WTRU 205 and the I-CSCF may transmit SIPregistration messages, subsequent call set-up requests and responses tothe S-CSCF 230. The P-CSCF 210 maintains a security association, forboth authentication and confidentiality. The P-CSCF 210 supportsemergency call local routing within the visited network, accounting,session timers and admission control.

The E-CSCF 215 may route emergency SIP requests to PSAPs. The E-CSCF 215receives the SIP request, determines the emergency services requestedand based upon the WTRUs 205 location, determines the PSAP address inorder to transmit the SIP request. The PSAP address may be resolvedthrough a combination of location and the type of emergency. The PSAP270 may reside in a public switched telephone network (PSTN) or may bean Internet protocol (IP) based PSAP. The E-CSCF 215 may directly sendthe SIP request to an IP based PSAP. If the PSAP 270 resides in thePSTN, the SIP request may be configured to be routed to the PSAP 270 viaan integrated services digital network (ISDN) user part (ISUP) request.The E-CSCF 215 uses Mw 262, Mg 256, Mi 266, Ml 252, Mm 268, Mx 258 andI4 250 reference points to connect to other IMS entities and other IPNetworks.

The Mm 268 reference point is a SIP-based reference point that connectsthe IMS to other IP-based multimedia networks. The Mw 262 referencepoint provides for an interface between the P-CSCF 210 and E-CSCF 215 orS-CSCF 230. The Mw 262 reference point may define the messages that areused between the CSCFs of any type in both the network operator's IMSand CSCFs in other network operators' IMSs.

The Mi 266 reference point may be used to complete a session to thecircuit-switched domain. The Mg 256 reference point links the mediagateway control function (MGCF), to the IMS. I4 250 may be used as areference point between an E-CSCF 215 and an EATF 235. I5 248 may beused as a reference point between an I-CSCF 275 and an EATF 235.

The AS 225 and S-CSCF 230 may be located in the home network. An ISC/Mw242 reference point may be used between the AS 225 and the S-CSCF 230.The S-CSCF 230 may act as a registrar for the WTRU 205 during IMSregistration. During an emergency registration, the WTRU 205 maytransmit an emergency signal via the P-CSCF 210 to the S-CSCF 230.

An emergency call establishment request may be transmitted by WTRU 205.WTRU 205 transmits a SIP INVITE request to the PSAP 270 in the visitednetwork via P-CSCF 210 and E-CSCF 215. By routing the emergency call viaa P-CSCF 210 and E-CSCF 215 in the visited network, the emergency callis handled by the visited network without involving WTRUs 205 homenetwork. The SIP INVITE request may be transmitted to the PSAP 270 whichmay be located in a PSTN. Interworking from the IMS to the PSTN may beperformed via the breakout gateway control function/media gatewaycontrol function (BGCF/MGCF).

Alternatively, the PSAP 270 maybe located in an IP based multimedianetwork. The SIP INVITE request may be transmitted to the PSAP 270 or toan Emergency Services Network (ESN) via an interconnection bordercontrol function internet protocol (IBCF/IP) multimedia network. TheIBCF provides overall control of the boundary between different serviceprovider networks and provides security for the IMS network.

The PSAP 270 may initiate an emergency callback to WTRU 205. The PSAP270 may transmit the callback signal to the WTRU 205 via the S-CSCF 230in the home network and the P-CSCF 210 in the visited network. The PSAP270 may use Mm 268, Mx 258 and Mw 262 reference points to connect to theS-CSCF 230. An emergency callback may be necessary if an originalemergency call was cut short, upon a loss of connection or on thecondition that the PSAP 270 requires a follow-up to the emergency callfor additional information, for example.

The PSAP 270 callback may be categorized as an emergency callback inorder to transmit the emergency callback to the WTRU that initiated theoriginal signal to which the callback is responding. The emergencycallback may be transmitted as a normal IMS incoming call and may besubject to subscribed services such as call forwarding. Subjecting thecallback to subscribed services may be disadvantageous and may preventthe callback from reaching the WTRU 205. By identifying callback, it maybe treated differently than other incoming calls. In addition,subscribed services may be disabled for callbacks.

Callbacks may be initiated by a PSAP 270 located in either a PSTN or IPnetwork. The PSAP 270 may initiate a communication with the LRF 220 inthe visited network in order to obtain additional location informationof the WTRU 205. A Le reference point 260 is used between the LRF 220and the PSAP 270.

The I-CSCF 275 may communicate with the WTRU via the EATF 235 in thevisited network. The I-CSCF 275 may interrogate an HSS in order todetermine which S-CSCF to route an incoming call. The EATF 235 maycommunicate with the WTRU 205 via the E-CSCF 215 and the P-CSCF 210.

The application server (AS) 225 may initiate an emergency call with theWTRU 205 via the S-CSCF 230 in the home network. The S-CSCF 230transmits the communication to the WTRU 205 via the E-CSCF 215 and theP-CSCF 210.

At any point in the method of FIG. 2, additional actions may beperformed between WTRU 205, P-CSCF 210, E-CSCF 215, LRF 220, EATF 235,S-CSCF 230, I-CSCF 275, PSAP 270 and AS 225.

FIG. 3 is a call flow diagram 300 of the communication of an indicatorfor callback in an emergency procedure. During an emergencyregistration, the WTRU 305 and the P-CSCF 310 receive an informationelement (IE) from the S-CSCF 320. The receipt of the IE occurs prior tothe transmission of an emergency call. A WTRU 305 may determine totransmit an emergency call request, and includes the received IE withthe emergency request.

Referring to FIG. 3, a WTRU 305 in a visited network may initiate aninitial unprotected emergency registration 322. A S-CSCF 320 maytransmit an authentication challenge to the WTRU 305. The WTRU 305transmits a protected SIP REGISTER message 324 for emergencyregistration to the S-CSCF 320 via the P-CSCF 310 in the visited networkand the I-CSCF 315 in the home network. The WTRU 305 may receive acallback indicator from the S-CSCF 320 upon successful registration. Inaddition, the P-CSCF 310 may act as a proxy for the WTRU 305 in thevisited network.

Once the I-CSCF 315 receives the SIP REGISTER message 324 from theP-CSCF 310, the I-CSCF 315 determines 326 the appropriate S-CSCF 320forthe WTRU 305 to register, using an interaction with the home subscriberserver (HSS). Once determined, the I-CSCF 315 transmits the SIP REGISTER324 to the appropriate S-CSCF 320. The S-CSCF 320 performsauthentication and registers 328 the identity of the WTRU 305 by bindingthe identity to contact header information.

The S-CSCF 320 creates a token piece of information, an IE, as the callback indicator, which may be used by a PSAP in an callback to a WTRU 305which initiated an emergency call. The S-CSCF 320 includes theinformation element in the SIP 200 (OK) response 330 transmitted to theWTRU 305 via the P-CSCF 310. The SIP 200 (OK) 330 may be transmitted inorder to indicate successful registration by the WTRU 305 with theS-CSCF 320. The indicator may be included in the contact header of theSIP 200 (OK) response 330. Other fields in the SIP 200 (OK) response mayalternatively be used to carry the callback indicator.

The indicator may also be included in a SIP INVITE request initiated bythe WTRU 305 in any emergency call. Additionally, the indicator may beincluded in any appropriate header field in any message that isexchanged between the WTRU 305 and the PSAP. On a condition that theindicator is unique based on the emergency registration, furthercorrelation may be required where the callback may be further verifiedas originating from a particular PSAP that received the emergency call.The indicator may be a parameter that includes a unique value.

The S-CSCF 320 sends the SIP 200 (OK) message 330 that includes the newindicator to the WTRU 305 via the I-CSCF 315 in the home network and theP-CSCF 310 in the visited network. The P-CSCF 310 stores the newindictor 332 with reference to the registered identity and contactaddress of the WTRU 305. By storing this information, the P-CSCF 310 isable to check, in the event of an emergency call initiated by the WTRU305, that the appropriate indicator is included in the emergency call tothe PSAP. For example, the WTRU 305 may initiate an emergency call, butmay not have included the indicator in the emergency message. On acondition that the WTRU 305 did not include the indicator, the P-CSCF310 includes the indictor in the emergency message. Further, on thecondition of a callback from a PSAP, the PSAP includes the indicator inthe callback request to the WTRU 305. The S-CSCF 320 that was involvedin the registration procedure will receive the callback from the PSAPand may suppress any subscribed services available to the WTRU 305 andmay direct the call to the WTRU 305 that initiated the emergency calland include the indicator.

At any point in the method of FIG. 3, additional actions may beperformed between WTRU 305, P-CSCF 310, C-CSCF 315 and S-CSCF 320.

FIG. 4 is a call flow diagram 400 of the transmission of an emergencycall that includes a callback indicator from a WTRU to a PSAP. Thecallback indicator may have been previously established in aregistration procedure, such as the procedure identified in FIG. 3.

Referring to FIG. 4, the WTRU 405 transmits a SIP INVITE request 428that includes a request URI with an urn:service:sos address and thecallback indicator to the PSAP 425 via the P-CSCF 410 and the E-CSCF415. The E-CSCF 415 resolves 430 the urn:service:sos address to aroutable address of a PSAP 425 that may be able to handle the requestedemergency service. The PSAP 425 may be in a PSTN or an IP network.

On a condition that the PSAP is located in an IP network, the E-CSCF 415transmits the SIP INVITE 428 that includes the request URI with asip:psap address and a call back indicator to the PSAP 425 located in anIP network 432. The request may be routed via border control entitiessuch as a IBCF 432.

Alternatively, the PSAP may be located in a PSTN and the E-CSCF 415transmits the SIP INVITE 428 that includes the request URI with asip:psap address and a call back indicator to the PSAP via a BGCF+MGCF420. The BGCF+MGCF 420 transmits an ISUP request for session setup 436to the PSAP 425 located in the PSTN.

In an embodiment, the WTRU 405 may not insert the callback indicator inthe call, since the WTRU 405 may not be aware that the call is anemergency call. Under normal procedures, the WTRU 405 may know that thecall that is initiated by the user is an emergency call. For example,WTRU 405 may recognize the dialed digits as an emergency service number.WTRU 405 may resolve the dialed digits to a service URN, which isincluded in the request URI of the SIP INVITE.

On a condition that WTRU 405 does not recognize the dialed digits as anemergency call, WTRU 405 may include the dialed digits in the requestURI. The P-CSCF 410 may detect that the dialed digits pertain to anemergency service, and may replace the dialed digits with theappropriate service URN.

The P-CSCF 410 may be aware that the call is an emergency call. TheP-CSCF 410 determines whether the call back indicator is present in thecall. On a condition that WTRU 405 may not have included the callbackindicator, the P-CSCF 410 may include the callback indicator receivedduring emergency registration. On a condition that emergencyregistration did not occur, an indicator may not exist.

The call back indicator may be included in a normal non-emergencyregistration, but may be policed by the P-CSCF 410 to only be includedin INVITE requests pertaining to emergency calls. This may preventmisuse by the WTRU 405 of the callback indicator in non-emergencyrequests.

The P-CSCF 410 may insert the callback indicator if a callback indicatoris stored for the emergency registered contact address and public useridentities that were registered during emergency registration for theWTRU 405.

At any point in the method of FIG. 4, additional actions may beperformed between WTRU 405, P-CSCF 410, E-CSCF 415, BGCF+MGCF 420 andPSAP 425.

FIG. 5 is a flow diagram 500 of an example of a new callback indicatorincluded in a PSAP callback from an IP based PSAP 525. The PSAP 525 maytransmit an SIP INVITE 528 for callback that includes a callbackindicator to the WTRU 505. The SIP INVITE 528 may be transmitted fromthe PSAP 525 to an I-CSCF 520 via IBCF. The I-CSCF 520 locates 530 theS-CSCF 515 at which the emergency caller, (e.g., WTRU), is registeredand routes the SIP INVITE 528 callback to the S-CSCF 515. The S-CSCF 515determines the emergency registered contact address of the WTRU 505 thatinitiated the emergency call in order to transmit the SIP INVITE 528callback and resolve the request URI. The S-CSCF 515 determines 530whether the callback indicator is the same as the one that was providedduring emergency registration. Terminating services may not be appliedto the call and the call is routed to the WTRU 505 that made theemergency call related to the SIP INVITE 528 callback.

The S-CSCF 515 transmits the SIP INVITE 528 for callback to the WTRU 505via the P-CSCF 510. The WTRU 505 may apply special processing 532 toensure callback is handled correctly. For example, the WTRU 505 maydisable services that may be applied to the call such as callforwarding, silent mode or the ability to place a call on hold.

At any point in the method of FIG. 5, additional actions may beperformed between WTRU 505, P-CSCF 510, S-CSCF 515, I-CSCF 520 and PSAP525.

FIGS. 6A and 6B are a call flow diagram 600 of an example of a newcallback indicator included in a PSAP callback from a PSTN based PSAP630. The PSAP 630 may transmit an ISUP call setup request 632 to theMGCF 625. On a condition that the MGCF 625 detects 634 that the ISUPcall setup request 632 is from the PSAP 630, it may insert a callingparty's category (CPC) value of callback in the SIP request 636 and maysend the SIP request 636 with the CPC value to the WTRU 605. The CPCindicates a callback from the PSAP 630 located in the PSTN. The CPC isan ISUP request parameter which is inserted by the MGCF 625 with a valueof callback in the P-Asserted-Identity header of the ISUP request 632.The MGCF 625 may use another parameter in another header field to alsoindicate a callback.

The MGCF 625 may detect the PSAP callback either through information inthe ISUP request 632 that may indicate the callback, or through a numberanalysis or trunk analysis, for example. The MGCF 625 may transmit theSIP INVITE 636 for call back that includes the CPC call back indicatorto the WTRU 605 via the I-CSCF 620. The I-CSCF 620 may locate 638 theS-CSCF 615 at which the emergency caller (for example, the WTRU 605) isregistered, and routes the request to the S-CSCF 615.

The S-CSCF 615 determines 640 the emergency registered contact addressof the WTRU 605 that initiated the emergency call in order to transmitthe SIP INVITE callback 636 and resolve the request URI. The S-CSCF 615determines whether the callback indicator is the same as the one thatwas provided during emergency registration. Terminating services may notbe applied to the call and the call is routed to the WTRU 605 that madethe emergency call related to the SIP INVITE callback 636.

The S-CSCF 615 transmits the SIP INVITE 636 for callback to the WTRU 605via the P-CSCF 610. The WTRU 605 may apply special processing to ensurecallback is handled correctly. For example, the WTRU 605 may disableservices 642 that may be applied to the call such as call forwarding.

At any point in the method of FIG. 6, additional actions may beperformed between WTRU 605, P-CSCF 610, S-CSCF 615, I-CSCF 620, MGCF 625and PSAP 630.

The procedures described in FIGS. 3-6B may be performed by the WTRU 102identified in FIG. 1B. The transceiver 120 may be configured but notlimited to transmitting the registration and emergency request messagesdescribed herein, while the processor 118 may be configured but notlimited to generating the request messages, processing the registrationresponse, storing the IE and suppressing subscribed services. Inaddition, the transceiver 120 may be configured but not limited toreceiving the registration response including an IE and receiving a PSAPcallback.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

1. A method for use in a wireless transmit/receive unit (WTRU), themethod comprising: transmitting, by the WTRU in a first network, aregistration message to a service call session control function (S-CSCF)in a second network; receiving, by the WTRU, a registration responseincluding an information element (IE) including a public safetyanswering point (PSAP) callback identifier, wherein the IE is stored bythe WTRU; transmitting, by the WTRU, an emergency call to the PSAP inthe second network, wherein the emergency call includes the PSAPcallback identifier; and receiving, by the WTRU, a callback from thePSAP, wherein the PSAP callback includes the PSAP callback identifier.2. The method of claim 1, wherein the registration message is anemergency registration request that includes authentication information.3. The method of claim 1, wherein the registration message istransmitted via a proxy call session control function (P-CSCF).
 4. Themethod of claim 1, wherein the registration response is received priorto transmission of the emergency call.
 5. The method of claim 1, whereinthe second network is an internet protocol (IP) Multimedia Subsystem(IMS) Network.
 6. The method of claim 1, wherein the second network is apublic switched telephone network (PSTN).
 7. A wireless transmit/receiveunit (WTRU) comprising: a transmitter configured to transmit aregistration message to a service call session control function (S-CSCF)in a second network; and a receiver configured to receive a registrationresponse including an information element (IE) including a public safetyanswering point (PSAP) callback identifier, wherein the IE is stored bythe WTRU; and wherein the transmitter is further configured to transmitan emergency call to the PSAP in the second network, wherein theemergency call includes the PSAP callback identifier; wherein thereceiver is further configured to receive a callback from the PSAP,wherein the callback includes the PSAP callback identifier; wherein theWTRU is located in a first network.
 8. The WTRU of claim 7 wherein theregistration message is an emergency registration request that includesauthentication information.
 9. The WTRU of claim 7 wherein theregistration message is transmitted via a proxy call session controlfunction (P-CSCF).
 10. The WTRU of claim 7 wherein the registrationresponse is received prior to transmission of an emergency call.
 11. TheWTRU of claim 7 wherein the second network is an internet protocol (IP)Multimedia Subsystem (IMS) Network.
 12. The WTRU of claim 7 wherein thesecond network is a public switched telephone network (PSTN).
 13. Apublic safety answering point (PSAP) comprising: a processor configuredto generate an information element (IE) including a PSAP callbackidentifier; a receiver configured to receive an emergency call from awireless transmit/receive unit (WTRU) in a first network, wherein theemergency call includes the PSAP callback identifier; and a transmitterconfigured to transmit a callback, wherein the callback includes thePSAP callback identifier; wherein the PSAP is located in a secondnetwork.
 14. A proxy call session control function (P-CSCF) comprising:a receiver configured to receive a registration message from a wirelesstransmit/receive unit (WTRU) in a first network; a transmitterconfigured to transmit the registration message to a service callsession control function (S-CSCF) in a second network; the receiverfurther configured to receive a registration response including aninformation element (IE) including a public safety answering point(PSAP) callback identifier, wherein the IE is stored by the P-CSCF; andwherein the receiver is further configured to receive an emergency callfrom the WTRU in the first network, wherein the emergency call includesthe PSAP callback identifier, and receive a callback from the PSAP,wherein the callback includes the PSAP callback identifier; wherein thetransmitter is further configured to transmit the emergency call to thePSAP in the second network, and transmit the callback to the WTRU;wherein the P-CSCF is located in the first network.
 15. The P-CSCF ofclaim 14 wherein the WTRU inserts the PSAP callback identifier in theemergency call.
 16. The P-CSCF of claim 14 wherein the P-CSCF insertsthe PSAP callback identifier in the emergency call.